An integrated circuit (IC) which is designed to be used as a motor controller IC is typically required to have an extra power supply voltage internally generated to drive the gates of the upper power devices of the output bridges of the IC. This internally generated voltage has to exceed the external power supply voltage to drive the gates of those devices (in source follower configurations) with enough overdrive voltage (Vgs-Vth) to minimize as much as possible the IC's drain-to-source "ON" resistance (RdsOn). Such a situation is highlighted in FIG. 1, in which the internally generated voltage (V.sub.boost) is shown driving the IC's output power devices.
The usual prior art approaches used to generate this internally generated voltage supply are shown in FIGS. 2 and 3. The prior art approach shown in FIG. 2 highlights a capacitive approach, while the FIG. 3 approach highlights an inductive approach. In maximum attainable voltage is 2V.sub.supply -2 V.sub.D, where "V.sub.D " is the diode drop that is about 0.75 Volts.
In FIG. 3, the V.sub.boost attainable voltage can be higher than that achieved in the circuit for FIG. 2 due to the current kick of the inductor. However, both of these circuits 5 present problems for IC designers due to the size of the capacitors needed to guarantee enough current capability to furnish V.sub.boost (current that the V.sub.boost can supply without dropping in voltage). These capacitors have to be added externally and cannot be integrated into the IC. The only component that can be integrated in the circuits shown in FIGS. 2 and 3 is the switch. Typically, the simplest way to design this voltage supply is using a CMOS power inverter. However, some drawbacks to these types of designs include possible transconductance, nonoptimized efficiency and the charging and discharging of external capacitors without control.
When designing these ICs, it is also important to find a way to clamp V.sub.boost at a certain voltage level due to the maximum voltages that the IC's design process can tolerate. In the above example, a typical MOS device (or DMOS device) can only have six volts as V.sub.GS (gate-to-source voltage), so V.sub.boost must be clamped as close as possible to the limit, be precise in temperature, and be without process variations. Therefore, in order to avoid reliability problems in production of the IC. A prior generation clamp design used a zener diode and a V.sub.BE (base-emitter) as the clamp. However, the total voltage variation of this prior design clamp was higher than one volt, therefore it did not afford much precision. A need exists for a charge pump voltage regulator that can provide good current capability, optimized efficiency and a precise voltage clamp to the voltage required.